U.S. patent application number 11/077281 was filed with the patent office on 2005-10-06 for dielectric ceramic composition, multilayer ceramic capacitor, and method for manufacturing the same.
This patent application is currently assigned to TDK CORPORATION. Invention is credited to Hara, Haruya, Iguchi, Toshihiro, Ito, Kazushige, Kojima, Takashi, Sato, Akira, Sato, Shigeki.
Application Number | 20050219794 11/077281 |
Document ID | / |
Family ID | 34840240 |
Filed Date | 2005-10-06 |
United States Patent
Application |
20050219794 |
Kind Code |
A1 |
Iguchi, Toshihiro ; et
al. |
October 6, 2005 |
Dielectric ceramic composition, multilayer ceramic capacitor, and
method for manufacturing the same
Abstract
A dielectric ceramic composition contains components, with
respective numbers of moles relative to 100 moles of barium
titanate, including barium titanate, a first sub-component
containing at least one oxide selected from a Mg oxide, a Ca oxide,
a Ba oxide, and Sr oxide, a second sub-component containing an
oxide containing 1 mol of Si atoms per mol, a third sub-component
containing at least one oxide selected from a V oxide, a Mo oxide,
and a W oxide, a fourth sub-component containing at least one
R.sup.1 oxide (wherein R.sup.1 is at least one selected from Sc,
Er, Tm, Yb, and Lu), a fifth sub-component containing at least one
R.sup.2 oxide (wherein R.sup.2 is at least one selected from Y, Dy,
Ho, Tb, Gd, and Eu), a sixth sub-component containing at least one
selected from a Mn oxide and a Cr oxide, and a seventh
sub-component containing at least one selected from calcium
zirconate and a mixture of a Ca oxide and Zr oxide. The ratio (A/B)
of the number of moles A of the second sub-component to the total
number of moles B of the fourth and fifth sub-components is 0.7 or
more. Alternatively, the ratio (C/D) of the number of moles C of Si
atoms in the second sub-component to the total number of moles of
the atoms in the first to seventh sub-components excluding the Si
atoms and oxygen atoms being 0.2 or more, and the total number of
moles of the fourth and fifth sub-components being 3 or more.
Inventors: |
Iguchi, Toshihiro; (Tokyo,
JP) ; Hara, Haruya; (Tokyo, JP) ; Ito,
Kazushige; (Tokyo, JP) ; Sato, Akira; (Tokyo,
JP) ; Sato, Shigeki; (Tokyo, JP) ; Kojima,
Takashi; (Tokyo, JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND, MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
TDK CORPORATION
Tokyo
JP
|
Family ID: |
34840240 |
Appl. No.: |
11/077281 |
Filed: |
March 11, 2005 |
Current U.S.
Class: |
361/321.2 |
Current CPC
Class: |
C04B 2235/3436 20130101;
C04B 2235/3454 20130101; H01G 4/30 20130101; C04B 2235/3225
20130101; C04B 2235/3239 20130101; C04B 2235/3241 20130101; C04B
2235/3262 20130101; C04B 35/64 20130101; C04B 35/62665 20130101;
C04B 2235/3208 20130101; C04B 2235/3217 20130101; H01G 4/1227
20130101; C04B 2235/3215 20130101; C04B 2235/3206 20130101; C04B
2235/3256 20130101; C04B 2235/6588 20130101; C04B 2235/6582
20130101; C04B 35/6303 20130101; C04B 2235/3213 20130101; C04B
2235/6584 20130101; C04B 2235/3205 20130101; C04B 35/4682 20130101;
C04B 2235/3249 20130101; C04B 2235/3224 20130101; C04B 2235/662
20130101; C04B 2235/3258 20130101; C04B 2235/6565 20130101 |
Class at
Publication: |
361/321.2 |
International
Class: |
H01G 004/06 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 16, 2004 |
JP |
P2004-73856 |
Mar 26, 2004 |
JP |
P2004-91221 |
Claims
What is claimed is:
1. A dielectric ceramic composition comprising components, with
respective numbers of moles relative to 100 moles of barium
titanate, including (a) barium titanate, (b) a first sub-component
comprising at least one oxide selected from a Mg oxide, a Ca oxide,
a Ba oxide, and Sr oxide with a number of moles of 0 to 7 in terms
of MgO, CaO, BaO, and SrO, respectively, (c) a second sub-component
comprising an oxide containing 1 mol of Si atoms per mol with a
number of moles of 0.5 to 12 in terms of the oxide, (d) a third
sub-component comprising at least one oxide selected from a V
oxide, a Mo oxide, and a W oxide with a number of moles of 0.01 to
0.5 in terms of V.sub.2O.sub.5, MoO.sub.3, WO.sub.3, respectively,
(e) a fourth sub-component comprising at least one R.sup.1 oxide
(wherein R.sup.1 is at least one selected from Sc, Er, Tm, Yb, and
Lu) with a number of moles of 0 to 7 in terms of
R.sup.1.sub.2O.sub.3, (f) a fifth sub-component comprising at least
one R.sup.2 oxide (wherein R.sup.2 is at least one selected from Y,
Dy, Ho, Tb, Gd, and Eu) with a number of moles of 0.5 to 9 in terms
of R.sup.2.sub.2O.sub.3, (g) a sixth sub-component comprising at
least one selected from a Mn oxide and a Cr oxide with a number of
moles of 0 to 0.5 in terms of MnO and Cr.sub.2O.sub.3,
respectively, and (h) a seventh sub-component comprising at least
one selected from calcium zirconate and a mixture of a Ca oxide and
Zr oxide with a number of moles of 0 to 5 in terms of CaZrO.sub.3
and CaO+ZrO.sub.3, respectively, wherein the ratio (A/B) of the
number of moles A of the second sub-component to the total number
of moles B of the fourth and fifth sub-components is 0.7 or
more.
2. The dielectric ceramic composition according to claim 1, wherein
the second sub-component is a compound oxide represented by (Ba,
Ca).sub.xSi.sub.2+x, and the number of moles of the compound oxide
is 2 to 10.
3. A multilayer ceramic capacitor comprising a laminate of
dielectric layers comprising the dielectric ceramic composition
according to claim 1 and internal electrode layers, the layers
being alternately stacked.
4. A dielectric ceramic composition comprising components in
respective number of moles relative to 100 moles of barium
titanate, the component including (a) barium titanate, (b) a first
sub-component comprising at least one oxide selected from a Mg
oxide, a Ca oxide, a Ba oxide, and Sr oxide with a number of moles
of 0 to 7 in terms of MgO, CaO, BaO, and SrO, respectively, (c) a
second sub-component comprising an oxide containing 1 mol of Si
atoms per mol with a number of moles of 0.5 to 12 in terms of the
oxide, (d) a third sub-component comprising at least one oxide
selected from a V oxide, a Mo oxide, and a W oxide with a number of
moles of 0.01 to 0.5 in terms of V.sub.2O.sub.5, MoO.sub.3,
WO.sub.3, respectively, (e) a fourth sub-component comprising at
least one R.sup.1 oxide (wherein R.sup.1 is at least one selected
from Sc, Er, Tm, Yb, and Lu) with a number of moles of 0 to 7 in
terms of R.sup.1.sub.2O.sub.3, (f) a fifth sub-component comprising
at least one R oxide (wherein R.sup.2 is at least one selected from
Y, Dy, Ho, Tb, Gd, and Eu) with a number of moles of 0.5 to 9 in
terms of R.sup.2.sub.2O.sub.3, (g) a sixth sub-component comprising
at least one selected from a Mn oxide and a Cr oxide with a number
of moles of 0 to 0.5 in terms of MnO and Cr.sub.2O.sub.3,
respectively, and (h) a seventh sub-component comprising at lease
one selected from calcium zirconate and a mixture of a Ca oxide and
Zr oxide with a number of moles of 0 to 5 in terms of CaZrO.sub.3
and CaO+ZrO.sub.3, respectively, wherein the ratio (C/D) of the
number of moles C of the Si atoms in the second sub-component to
the total number of moles D of the atoms in the first to the
seventh sub-components excluding the Si atoms and oxygen atoms is
0.2 or more, and the total number of moles of the fourth and fifth
sub-components is 3 or more.
5. The dielectric ceramic composition according to claim 4, wherein
the ratio (C/D) of the number of moles C of the Si atoms in the
second sub-component to the total number of moles D of the atoms in
the first to the seventh sub-components excluding the Si atoms and
oxygen atoms is 0.2 or more and less than 0.24.
6. A multilayer ceramic capacitor comprising a laminate of
dielectric layers comprising the dielectric ceramic composition
according to claim 4 and internal electrode layers, the layers
being alternately stacked.
7. A method for manufacturing a multilayer ceramic capacitor
comprising: a step of preparing a dielectric ceramic composition
raw material comprising basic components including (1) barium
titanate and/or a compound or a mixture converted to barium
titanate by firing, (2) a first sub-component comprising at least
one oxide selected from MgO, CaO, BaO, and SrO and/or a compound
converted to the oxide by firing, (3) a second sub-component
comprising an oxide containing 1 mol of Si atoms per mol, (4) a
third sub-component comprising at least one oxide selected from
V.sub.2O.sub.5, MoO.sub.3, WO.sub.3 and/or a compound converted to
the oxide by firing, (5) a fourth sub-component comprising at least
one oxide represented by R.sup.1.sub.2O.sub.3 (wherein R.sup.1 is
an element from Sc, Er, Tm, Yb, and Lu) and/or a compound converted
to the oxide by firing, (6) a fifth sub-component comprising at
least one oxide represented by R.sup.2.sub.2O.sub.3 (wherein
R.sup.2 is at least one selected from Y, Dy, Ho, Tb, Gd, and Eu)
and/or a compound converted to the oxide by firing, (7) a sixth
sub-component comprising at least one oxide selected from MnO and
Cr.sub.2O.sub.3 and/or a compound converted to the oxide by firing,
and (8) a seventh sub-component comprising at least one compound
selected from CaZrO.sub.3, a mixture of CaO and ZrO.sub.2, a
compound converted to CaZrO.sub.3 by firing, and a mixture of
compounds converted to CaO and ZrO.sub.2, respectively, by firing,
the numbers of moles of the first, second, third, fourth, fifth,
sixth, and seventh sub-components relative to 100 moles of the
barium titanate being 0 to 7, 0.5 to 12, 0.01 to 0.5, 0 to 7, 0.5
to 9, 0 to 0.5, and 0 to 5, respectively, in terms of the
respective oxides, and the ratio (A/B) of the number of moles A of
the second sub-component to the total number of moles B of the
fourth and fifth sub-components being 0.7 or more; a step of firing
a laminate produced by alternately stacking green sheets for
forming dielectric layers and paste layers for forming internal
electrode layers, the green sheets being formed using the
dielectric ceramic composition raw material, to form a ceramic chip
in which the green sheets become the dielectric layers, and the
paste layers become the internal electrode layers; and a step of
re-oxidizing the dielectric layers in the ceramic chip.
8. The method for manufacturing a multilayer ceramic capacitor
according to claim 7, wherein the second sub-component is a
compound oxide represented by (Ba, Ca).sub.xSiO.sub.2+x, and has a
number of moles of 2 to 10.
9. A method for manufacturing a multilayer ceramic capacitor
comprising: a step of preparing a dielectric ceramic composition
raw material comprising components including (1) barium titanate
and/or a compound or a mixture converted to barium titanate by
firing, (2) a first sub-component comprising at least one oxide
selected from MgO, CaO, BaO, and SrO and/or a compound converted to
the oxide by firing, (3) a second sub-component comprising an oxide
containing 1 mol of Si atoms per mol, (4) a third sub-component
comprising at least one oxide selected from V.sub.2O.sub.5,
MoO.sub.3, WO.sub.3 and/or a compound converted to the oxide by
firing, (5) a fourth sub-component comprising at least one oxide
represented by R.sup.1.sub.2O.sub.3 (wherein R.sup.1 is an element
from Sc, Er, Tm, Yb, and Lu) and/or a compound converted to the
oxide by firing, (6) a fifth sub-component comprising at least one
oxide represented by R.sup.2.sub.2O.sub.3 (wherein R.sup.2 is at
least one selected from Y, Dy, Ho, Tb, Gd, and Eu) and/or a
compound converted to the oxide by firing, (7) a sixth
sub-component comprising at least one oxide selected from MnO and
Cr.sub.2O.sub.3 and/or a compound converted to the oxide by firing,
and (8) a seventh sub-component comprising at least one compound
selected from CaZrO.sub.3, a mixture of CaO and ZrO.sub.2, a
compound converted to CaZrO.sub.3 by firing, and a mixture of
compounds converted to CaO and ZrO.sub.2, respectively, by firing,
the numbers of moles of the first, second, third, fourth, fifth,
sixth, and seventh sub-components relative to 100 moles of the
barium titanate being 0 to 7, 0.5 to 12, 0.01 to 0.5, 0 to 7, 0.5
to 9, 0 to 0.5, and 0 to 5, respectively, in terms of the
respective oxides, the ratio (C/D) of the number of moles C of Si
atoms in the second sub-component to the total number of moles of
the atoms in the first to seventh sub-components excluding the Si
atoms and oxygen atoms being 0.2 or more, and the total number of
moles of the fourth and fifth sub-components being 3 or more; a
step of firing a laminate produced by alternately stacking green
sheets for forming dielectric layers and paste layers for forming
internal electrode layers, the green sheets being formed using the
dielectric ceramic composition raw material, to form a ceramic chip
in which the green sheets become the dielectric layers, and the
paste layers become the internal electrode layers; and a step of
re-oxidizing the dielectric layers in the ceramic chip.
10. The method for manufacturing a dielectric ceramic composition
according to claim 9, wherein the ratio (C/D) of the number of
moles C of the Si atoms in the second sub-component to the total
number of moles D of the atoms in the first to the seventh
sub-components excluding the Si atoms and oxygen atoms is 0.2 or
more and less than 0.24.
11. A dielectric ceramic composition raw material comprising basic
components including (1) barium titanate and/or a compound or a
mixture converted to barium titanate by firing, (2) a first
sub-component comprising at least one oxide selected from MgO, CaO,
BaO, and SrO and/or a compound converted to the oxide by firing,
(3) a second sub-component comprising an oxide containing 1 mol of
Si atoms per mol, (4) a third sub-component comprising at least one
oxide selected from V.sub.2O.sub.5, MoO.sub.3, WO.sub.3 and/or a
compound converted to the oxide by firing, (5) a fourth
sub-component comprising at least one oxide represented by
R.sup.1.sub.2O.sub.3 (wherein R.sup.1 is an element from Sc, Er,
Tm, Yb, and Lu) and/or a compound converted to the oxide by firing,
(6) a fifth sub-component comprising at least one oxide represented
by R.sup.2.sub.2O.sub.3 (wherein R.sup.2 is at least one selected
from Y, Dy, Ho, Tb, Gd, and Eu) and/or a compound converted to the
oxide by firing, (7) a sixth sub-component comprising at least one
oxide selected from MnO and Cr.sub.2O.sub.3 and/or a compound
converted to the oxide by firing, and (8) a seventh sub-component
comprising at least one compound selected from CaZrO.sub.3, a
mixture of CaO and ZrO.sub.2, a compound converted to CaZrO.sub.3
by firing, and a mixture of compounds converted to CaO and
ZrO.sub.2, respectively, by firing, the numbers of moles of the
first, second, third, fourth, fifth, sixth, and seventh
sub-components relative to 100 moles of the barium titanate being 0
to 7, 0.5 to 12, 0.01 to 0.5, 0 to 7, 0.5 to 9, 0 to 0.5, and 0 to
5, respectively, in terms of the respective oxides, and the ratio
(A/B) of the number of moles A of the second sub-component to the
total number of moles B of the fourth and fifth sub-components
being 0.7 or more.
12. A dielectric ceramic composition raw material comprising basic
components including (1) barium titanate and/or a compound or a
mixture converted to barium titanate by firing, (2) a first
sub-component comprising at least one oxide selected from MgO, CaO,
BaO, and SrO and/or a compound converted to the oxide by firing,
(3) a second sub-component comprising an oxide containing 1 mol of
Si atoms per mol, (4) a third sub-component comprising at least one
oxide selected from V.sub.2O.sub.5, MoO.sub.3, WO.sub.3 and/or a
compound converted to the oxide by firing, (5) a fourth
sub-component comprising at least one oxide represented by
R.sup.1.sub.2O.sub.3 (wherein R.sup.1 is an element from Sc, Er,
Tm, Yb, and Lu) and/or a compound converted to the oxide by firing,
(6) a fifth sub-component comprising at least one oxide represented
by R.sup.2.sub.2O.sub.3 (wherein R.sup.2 is at least one selected
from Y, Dy, Ho, Tb, Gd, and Eu) and/or a compound converted to the
oxide by firing, (7) a sixth sub-component comprising at least one
oxide selected from MnO and Cr.sub.2O.sub.3 and/or a compound
converted to the oxide by firing, and (8) a seventh sub-component
comprising at least one compound selected from CaZrO.sub.3, a
mixture of CaO and ZrO.sub.2, a compound converted to CaZrO.sub.3
by firing, and a mixture of compounds converted to CaO and
ZrO.sub.2, respectively, by firing, the number of moles of the
first, second, third, fourth, fifth, sixth, and seventh
sub-components relative to 100 moles of the barium titanate being 0
to 7, 0.5 to 12, 0.01 to 0.5, 0 to 7, 0.5 to 9, 0 to 0.5, and 0 to
5, respectively, in terms of the respective oxides, the ratio (C/D)
of the number of moles C of Si atoms in the second sub-component to
the total number of moles of the atoms in the first to seventh
sub-components excluding the Si atoms and oxygen atoms being 0.2 or
more, and the total number of moles of the fourth and fifth
sub-components being 3 or more.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a dielectric ceramic
composition, a multilayer ceramic capacitor, and a method for
manufacturing the same. More specifically, the present invention
relates to a dielectric ceramic composition and a multilayer
ceramic capacitor having a long mean time to failure (MTTF) and
satisfactory X8R characteristic.
[0003] 2. Description of the Related Art
[0004] Multilayer ceramic capacitors are widely used as small,
large-capacity electronic components having high reliability. In
recent years, demands for multilayer ceramic capacitors to have
smaller sizes, lower cost, and higher capacity and reliability have
become more and more strict with miniaturization and advancement of
performance of apparatuses.
[0005] A multilayer ceramic capacitor is generally manufactured by
stacking internal electrode layers and dielectric layers using a
paste for internal electrode layers and a paste for dielectric
layers, respectively, by a sheet method, a printing method, or the
like to form a laminate, and then simultaneously firing the
internal electrode layers and the dielectric layers in the
laminate.
[0006] Although Pd or a Pd alloy is generally used as a conductive
material for the internal electrode layers, a base metal such as
relatively inexpensive Ni or a Ni alloy is increasingly used
because Pd is expensive. When a base metal is used as a conductive
material for the internal electrode layers, the internal electrode
layers are oxidized by firing in air. Therefore, the dielectric
layers and the internal electrode layers must be simultaneously
fired in a reducing atmosphere. However, the dielectric layers are
reduced by firing in the reducing atmosphere to decrease the
resistivity. Therefore, an irreducible dielectric material has been
developed.
[0007] However, a multilayer ceramic capacitor using an irreducible
dielectric material has the problem that the insulation resistance
(IR) is significantly decreased by application of an electric field
(i.e., short IR life), and the reliability is low. It is thus
demanded to solve the problem.
[0008] Furthermore, a capacitor is also required to have excellent
temperature characteristics, and particularly the temperature
characteristics are required to be flat under severe conditions
according to applications. In recent, a multilayer ceramic
capacitor has been used in various electronic apparatuses such as
an engine electron control unit (ECU) mounted in an automobile
engine room, a crank angle sensor, an antilock brake system (ABS)
module, and the like. These electronic apparatuses are adapted for
stable engine control, drive control, and brake control, and thus
the circuits thereof are required to have high temperature
stability.
[0009] The electronic apparatuses are used in an environment in
which the temperature in a cold district is estimated to decrease
to about -20.degree. C. or less in winter, and the temperature
after the start of an engine is estimated to increase to about
+130.degree. C. in summer. There has recently been a tendency to
omit a wire harness for connecting an electronic apparatus and an
apparatus to be controlled. In some cases, therefore, an electronic
apparatus is installed outside a car, and the environment of the
electronic apparatus becomes more and more severe. Therefore, a
capacitor used for the electronic apparatuses is required to have
flat temperature characteristics over a wide temperature range.
[0010] A composition known as a dielectric ceramic composition
having a high dielectric constant and flat capacitance-temperature
characteristics contains BaTiO.sub.3 as a main component and
Nb.sub.2O.sub.5--CO.sub.3O.s- ub.4, MgO--Y, a rare earth element
(Dy, Ho, or the like), Bi.sub.2O.sub.3--TiO.sub.2, and the like.
However, such a BaTiO.sub.3-based high dielectric constant material
cannot satisfy the X7R characteristic (.DELTA.C/C=.+-.15% at
-55.degree. C. to 125.degree. C.) stipulated in the EIA standard,
and thus the material cannot be applied to an automobile electronic
apparatus used in the above-described severe environment. A
dielectric ceramic composition satisfying the X8R characteristic
(.DELTA.C/C=.+-.15% at -55.degree. C. to 150.degree. C.) stipulated
in the EIA standard is required for the above-described electronic
apparatus.
[0011] The applicant has previously proposed a dielectric ceramic
composition which has a high dielectric constant, satisfies the X8R
characteristic, and permits firing in a reducing atmosphere, and
which will be described below (refer to, for example, Japanese
Patent Nos. 3,348,081 and 3,341,003).
[0012] Japanese Patent No. 3,348,081 discloses a dielectric ceramic
composition prepared from a raw material containing at least a main
component comprising barium titanate, a first sub-component
comprising at least one selected from MgO, CaO, BaO, SrO, and
Cr.sub.2O.sub.3, a second sub-component mainly comprising silicon
oxide, a third sub-component comprising at least one selected from
V.sub.2O.sub.5, MoO.sub.3, and WO.sub.3, and a fourth sub-component
comprising an R.sup.1 oxide (wherein R.sup.1 is at least one
selected from Sc, Er, Tm, Yb, and Lu), and a fifth sub-component
comprising CaZrO.sub.3 or CaO+ZrO.sub.2. The ratios of the
respective components to 100 moles of the main component are: the
first sub-component, 0.1 to 3 moles; the second sub-component, 2 to
10 moles; the third sub-component, 0.01 to 0.5 mole; the fourth
sub-component, 0.5 to 7 moles (in terms of R.sup.1); and the fifth
sub-component, 0<fifth sub-component.ltoreq.5 moles.
[0013] Japanese Patent No. 3,341,003 discloses a dielectric ceramic
composition prepared from a raw material comprising at least a main
component comprising barium titanate, a first sub-component
comprising an AE oxide (wherein AE is at least one selected from
Mg, Ca, Ba, and Sr), and a second sub-component comprising an R
oxide (wherein R is at least one selected from Y, Dy, Ho, and Er).
The ratios of the respective components to 100 moles of the main
component are: the first sub-component, 0<first
sub-component<0.1 mole; and the second sub-component, 1
mole<second sub-component<7 moles.
[0014] The dielectric ceramic compositions disclosed in Japanese
Patent Nos. 3,348,081 and 3,341,003 have a high dielectric constant
and capacitance-temperature characteristics satisfying the X8R
characteristic (.DELTA.C/C=.+-.15% at -55.degree. C. to 150.degree.
C.) stipulated in the EIA standard, and can be fired in a reducing
atmosphere because Pb, Bi, Zn, and the like are not contained.
However, the dielectric ceramic compositions disclosed in Japanese
Patent Nos. 3,348,081 and 3,341,003 do not necessarily show a
satisfactorily long mean time to failure when a dielectric layer is
thinned for further miniaturizing a multilayer ceramic capacitor
and increasing the capacitance. The compositions are also
disadvantageous in that a dielectric ceramic composition exhibiting
a small variation in means time to failure cannot be easily
produced.
SUMMARY OF THE INVENTION
[0015] The present invention has been achieved for solving the
above-described problems. A first object of the present invention
is to provide a dielectric ceramic composition and a multilayer
ceramic capacitor comprising the dielectric ceramic composition
which has a long mean time to failure and capacitance-temperature
characteristics satisfying the X8R characteristic stipulated in the
EIA standard when a dielectric layer is further thinned for
decreasing a size and increasing capacitance.
[0016] A second object of the present invention is to provide a
dielectric ceramic composition and a multilayer ceramic capacitor
comprising the dielectric ceramic composition which has a long mean
time to failure and a small variation in lifetime, and
capacitance-temperature characteristics satisfying the X8R
characteristic stipulated in the EIA standard.
[0017] A third object of the present invention is to provide a
method for manufacturing the multilayer ceramic capacitor.
[0018] A fourth object of the present invention is to provide a raw
material used for preparing the dielectric ceramic composition.
[0019] In order to achieve the first to fourth objects, a
dielectric ceramic composition of the present invention comprises
basic components, with respective numbers of moles relative to 100
moles of barium titanate, including (a) barium titanate, (b) a
first sub-component comprising at least one selected from a Mg
oxide, a Ca oxide, a Ba oxide, and Sr oxide with a number of moles
of 0 to 7 in terms of MgO, CaO, BaO, and SrO, respectively, (c) a
second sub-component comprising an oxide containing 1 mol of Si
atoms per mol with a number of moles of 0.5 to 12 in terms of the
oxide, (d) a third sub-component comprising at least one selected
from a V oxide, a Mo oxide, and a W oxide with a number of moles of
0.01 to 0.5 in terms of V.sub.2O.sub.5, MoO.sub.3, WO.sub.3,
respectively, (e) a fourth sub-component comprising at least one
R.sup.1 oxide (wherein R.sup.1 is at least one selected from Sc,
Er, Tm, Yb, and Lu) with a number of moles of 0 to 7 in terms of
R.sup.1.sub.2O.sub.3, (f) a fifth sub-component comprising at least
one R oxide (wherein R.sup.2 is at least one selected from Y, Dy,
Ho, Tb, Gd, and Eu) with a number of moles of 0.5 to 9 in terms of
R.sup.2.sub.2O.sub.3, (g) a sixth sub-component comprising at least
one selected from a Mn oxide and a Cr oxide with a number of moles
of 0 to 0.5 in terms of MnO and Cr.sub.2O.sub.3, respectively, and
(h) a seventh sub-component comprising at least one selected from
calcium zirconate and a mixture of a Ca oxide and Zr oxide with a
number of moles of 0 to 5 in terms of CaZrO.sub.3 and
CaO+ZrO.sub.2, respectively.
[0020] A dielectric ceramic composition and a multilayer ceramic
capacitor including a dielectric layer comprising the dielectric
ceramic composition of the present invention contain the
above-described basic components, and the characteristics thereof,
such as the X8R characteristic, mean time to failure, variation in
lifetime, and the like, can be improved by controlling the
composition of the basic components.
[0021] In order to achieve the first object, a dielectric ceramic
composition (referred to as a "dielectric ceramic composition I"
hereinafter) of the present invention comprises the above-described
basic components, wherein the ratio (A/B) of the number of moles A
of the second sub-component to the total number of moles B of the
fourth and fifth sub-components is 0.7 or more.
[0022] In the barium titanate-based dielectric ceramic composition
I containing the above-described sub-components, when the ratio
(A/B) of the number of moles A of the second sub-component to the
total number of moles B of the fourth and fifth sub-components is
0.7 or more, the X8R characteristic is satisfied, and the mean time
to failure is long. In a conventional barium titanate-based
dielectric ceramic composition, when an electric field is applied,
oxygen defects present in a dielectric material move to break down
the insulation of the dielectric material. Therefore, rare earth
elements (R.sup.1 atoms and R.sup.2 atoms) functioning as a donor
are added for preventing the movement of the oxygen defects.
Although the addition of the rare earth element increases the time
to breakdown of insulation, the addition of a large amount of rare
earth elements may cause half-baking and may in turn decrease the
lifetime. In the present invention, in order to prevent this
problem, the ratio of the second sub-component functioning as a
sintering aid to the total of the fourth and fifth sub-components
comprising rare earth elements functioning as a donor is controlled
in the above-described range, thereby producing the dielectric
ceramic composition 1 having a long mean time to failure.
[0023] In the dielectric ceramic composition I of the present
invention, preferably, the second sub-component is a compound oxide
represented by (Ba, Ca).sub.xSi.sub.2+x, and the number of moles of
the compound oxide is 2 to 10.
[0024] A multilayer ceramic capacitor (referred to as a "multilayer
ceramic capacitor I" hereinafter) of the present invention
comprises a laminate of dielectric layers comprising the dielectric
ceramic composition I of the present invention and internal
electrode layers, the layers being alternately stacked.
[0025] The multilayer ceramic capacitor I of the present invention
comprising the laminate the dielectric layers comprising the
dielectric ceramic composition I of the present invention and the
internal electrode layers, the layers being alternately stacked,
satisfies the X8R characteristic and has a long mean time to
failure.
[0026] In order to achieve the second object, a dielectric ceramic
composition (referred to as a "dielectric ceramic composition II"
hereinafter) of the present invention comprises the above-described
basic components wherein the ratio (C/D) of the number of moles C
of the Si atoms in the second sub-component to the total number of
moles D of the atoms in the first to the seventh sub-components
excluding the Si atoms and oxygen atoms is 0.2 or more, and the
total number of moles of the fourth and fifth sub-components is 3
or more.
[0027] In the barium titanate-based dielectric ceramic composition
II containing the above-described sub-components according to the
present invention, when the ratio (C/D) of the number of moles C of
the Si atoms in the second sub-component to the total number of
moles D of the atoms in the first to the seventh sub-components
excluding the Si atoms and oxygen atoms is 0.2 or more, and the
total number of moles of the fourth and fifth sub-components is 3
or more, the X8R characteristic is satisfied, and the mean time to
failure is long. This is possibly because the fourth and fifth
sub-components function as donor components for preventing movement
of oxygen defects, and the C/D ratio is set to 0.2 or more to
increase the amount of Si functioning as a grain boundary
component, thereby increasing the electric field applied to grain
boundaries and avoiding application of the electric field to the
insides of grains.
[0028] In the dielectric ceramic composition II of the present
invention, the ratio (C/D) of the number of moles C of the Si atoms
in the second sub-component to the total number of moles D of the
atoms in the first to the seventh sub-components excluding the Si
atoms and oxygen atoms is preferably 0.2 or more and less than
0.24. In addition to the above-described effect, the dielectric
ceramic composition II of the present invention has the effect that
a segregation layer is little formed at a grain boundary triple
point because the ratio C/D is less than 0.24, thereby decreasing
the variation in lifetime.
[0029] A multilayer ceramic capacitor (referred to as a "multilayer
ceramic capacitor II" hereinafter) of the present invention
comprises a laminate of dielectric layers comprising the dielectric
ceramic composition II of the present invention and internal
electrode layers, the layers being alternately stacked.
[0030] The multilayer ceramic capacitor II of the present invention
comprising the laminate of the dielectric layers comprising the
dielectric ceramic composition II of the present invention and the
internal electrode layers, the layers being alternately stacked,
satisfies the X8R characteristic, and has a long mean time to
failure and a small variation in lifetime.
[0031] In order to achieve the third object, a method for
manufacturing the multilayer ceramic capacitor I of the present
invention comprises a step of preparing a dielectric ceramic
composition raw material I comprising basic components including
(1) barium titanate and/or a compound or a mixture converted to
barium titanate by firing, (2) a first sub-component comprising at
least one oxide selected from MgO, CaO, BaO, and SrO and/or a
compound converted to the oxide by firing, (3) a second
sub-component comprising an oxide containing 1 mole of Si atoms per
mole, (4) a third sub-component comprising at least one oxide
selected from V.sub.2O.sub.5, MoO.sub.3, WO.sub.3 and/or a compound
converted to the oxide by firing, (5) a fourth sub-component
comprising at least one oxide represented by R.sup.1.sub.2O.sub.3
(wherein R.sup.1 is an element selected from Sc, Er, Tm, Yb, and
Lu) and/or a compound converted to the oxide by firing, (6) a fifth
sub-component comprising at least one oxide represented by
R.sup.2.sub.2O.sub.3 (wherein R.sup.2 is at least one selected from
Y, Dy, Ho, Tb, Gd, and Eu) and/or a compound converted to the oxide
by firing, (7) a sixth sub-component comprising at least one oxide
selected from MnO and Cr.sub.2O.sub.3 and/or a compound converted
to the oxide by firing, and (8) a seventh sub-component comprising
at least one compound selected from CaZrO.sub.3, a mixture of CaO
and ZrO.sub.2, a compound converted to CaZrO.sub.3 by firing, and a
mixture of compounds converted to CaO and ZrO.sub.2, respectively,
by firing, the numbers of moles of the first, second, third,
fourth, fifth, sixth, and seventh sub-components relative to 100
moles of the barium titanate being 0 to 7, 0.5 to 12, 0.01 to 0.5,
0 to 7, 0.5 to 9, 0 to 0.5, and 0 to 5, respectively, in terms of
the respective oxides, and the ratio (A/B) of the number of moles A
of the second sub-component to the total number of moles B of the
fourth and fifth sub-components being 0.7 or more; a step of firing
a laminate produced by alternately stacking green sheets for
forming dielectric layers and paste layers for forming internal
electrode layers, the green sheets being formed using the
dielectric ceramic composition raw material I, to form a ceramic
chip in which the green sheets become the dielectric layers and the
paste layers become the internal electrode layers; and a step of
re-oxidizing the dielectric layers in the ceramic chip.
[0032] In the present invention, the dielectric ceramic composition
raw material I is prepared, in which the ratio (A/B) of the number
of moles A of the second sub-component functioning as a sintering
aid to the total number of moles B of the fourth and fifth
sub-components comprising rare earth elements functioning as donors
is 0.7 or more. Therefore, the multilayer ceramic capacitor
produced using the raw material I satisfies the X8R characteristic
and has a long mean time to failure.
[0033] In the method for manufacturing the multilayer ceramic
capacitor I of the present invention, preferably, the second
sub-component is a compound oxide represented by (Ba,
Ca).sub.xSiO.sub.2+x, and has a number of moles of 2 to 10.
[0034] In order to achieve the third object, a method for
manufacturing the multilayer ceramic capacitor II of the present
invention comprises a step of, preparing a dielectric ceramic
composition raw material II containing the same basic components as
those of the dielectric ceramic composition raw material I for
manufacturing the multilayer ceramic capacitor I, the ratio (C/D)
of the number of moles C of Si atoms in the second sub-component to
the total number of moles of the atoms in the first to seventh
sub-components excluding the Si atoms and oxygen atoms being 0.2 or
more, and the total number of moles of the fourth and fifth
sub-components being 3 moles or more; a step of firing a laminate
produced by alternately stacking green sheets for forming
dielectric layers and paste layers for forming internal electrode
layers, the green sheets being formed using the dielectric ceramic
composition raw material II, to form a ceramic chip in which the
green sheets become the dielectric layers and the paste layers
become the internal electrode layers; and a step of re-oxidizing
the dielectric layers in the ceramic chip.
[0035] The multilayer ceramic capacitor II manufactured using the
raw material satisfies the X8R characteristic and has a long mean
time to failure and a small variation in lifetime.
[0036] In order to achieve the fourth object, a dielectric ceramic
composition raw material I of the present invention comprises basic
components including (1) barium titanate and/or a compound or a
mixture converted to barium titanate by firing, (2) a first
sub-component comprising at least one oxide selected from MgO, CaO,
BaO, and SrO and/or a compound converted to the oxide by firing,
(3) a second sub-component comprising an oxide containing 1 mol of
Si atoms per mol, (4) a third sub-component comprising at least one
oxide selected from V.sub.2O.sub.5, MoO.sub.3, WO.sub.3 and/or a
compound converted to the oxide by firing, (5) a fourth
sub-component comprising at least one oxide represented by
R.sup.1.sub.2O.sub.3 (wherein R.sup.1 is an element from Sc, Er,
Tm, Yb, and Lu) and/or a compound converted to the oxide by firing,
(6) a fifth sub-component comprising at least one oxide represented
by R.sup.2.sub.2O.sub.3 (wherein R.sup.2 is at least one selected
from Y, Dy, Ho, Tb, Gd, and Eu) and/or a compound converted to the
oxide by firing, (7) a sixth sub-component comprising at least one
oxide selected from MnO and Cr.sub.2O.sub.3 and/or a compound
converted to the oxide by firing, and (8) a seventh sub-component
comprising at least one compound selected from CaZrO.sub.3, a
mixture of CaO and ZrO.sub.2, a compound converted to CaZrO.sub.3
by firing, and a mixture of compounds converted to CaO and
ZrO.sub.2, respectively, by firing, the numbers of moles of the
first, second, third, fourth, fifth, sixth, and seventh
sub-components relative to 100 moles of the barium titanate being 0
to 7, 0.5 to 12, 0.01 to 0.5, 0 to 7, 0.5 to 9, 0 to 0.5, and 0 to
5; respectively, in terms of the respective oxides, and the ratio
(A/B) of the number of moles A of the second sub-component to the
total number of moles B of the fourth and fifth sub-components
being 0.7 or more.
[0037] In order to achieve the fourth object, a dielectric ceramic
composition raw material II comprises the same basic components as
those of the dielectric ceramic composition raw material I, wherein
the ratio (C/D) of the number of moles C of Si atoms in the second
sub-component to the total number of moles of the atoms in the
first to seventh sub-components excluding the Si atoms and oxygen
atoms is 0.2 or more, and the total number of moles of the fourth
and fifth sub-components is 3 moles or more.
[0038] As described above, in the dielectric ceramic composition I
and the multilayer ceramic capacitor I of the present invention,
the amounts of the sintering aid for preventing half-baking and the
rare earth elements functioning as donors are controlled as
described above. Therefore, the dielectric ceramic composition I
and the multilayer ceramic capacitor I have a long mean time to
failure and capacitance-temperature characteristics satisfying the
X8R characteristic (.DELTA.C/C=.+-.15% at -55.degree. C. to
150.degree. C.) stipulated in the EIA standard. Therefore, when a
dielectric layer is further thinned for decreasing size and
increasing capacitance, availability becomes significant, and
particularly the dielectric ceramic composition I and the
multilayer ceramic capacitor I are effective in application to
automobiles used in severe environments.
[0039] Also, in the dielectric ceramic composition II and the
multilayer ceramic capacitor II of the present invention, the ratio
of the second sub-component functioning as the sintering aid to the
other sub-components is controlled as described above, and the
total amount of the rare earth components is controlled in the
above-described range. Therefore, the dielectric ceramic
composition II and the multilayer ceramic capacitor II have a long
mean time to failure, a small variation in lifetime, and
capacitance-temperature characteristics satisfying the X8R
characteristic (.DELTA.C/C=.+-.15% at -55.degree. C. to 150.degree.
C.) stipulated in the EIA standard. Therefore, when a dielectric
layer is further thinned for decreasing size and increasing
capacitance, the availability becomes significant, and particularly
the dielectric ceramic composition II and the multilayer ceramic
capacitor II with high reliability can be applied to automobiles
used in severe environments.
[0040] The dielectric ceramic composition raw materials (I and II)
and the dielectric ceramic compositions (I and II) of the present
invention do not contain Pb, Bi, Zn, and the like, and can thus be
fired in a reducing atmosphere. There is also the effect that the
capacitance less changes with time under a. DC electric field.
[0041] The method for manufacturing the multilayer ceramic
capacitor I is capable of manufacturing a multilayer ceramic
capacitor I having a long mean time to failure and satisfying the
X8R characteristic. Also, the method for manufacturing the
multilayer ceramic capacitor II is capable of manufacturing a
multilayer ceramic capacitor II satisfying the X8R characteristic
and having a long mean time to failure and a small variation in
lifetime.
BRIEF DESCRIPTION OF THE DRAWINGS
[0042] FIG. 1 is a partially cut-way perspective view schematically
showing an example of a multilayer ceramic capacitor of the present
invention; and
[0043] FIG. 2 is a sectional view schematically showing the basic
structure of a multilayer ceramic capacitor of the present
invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0044] A dielectric ceramic composition, a method for producing the
dielectric ceramic composition, a multilayer ceramic capacitor, and
a raw material for the dielectric ceramic composition according to
the present invention will be described below. The scope of the
present invention is not limited by the embodiments described
below.
[0045] (Multilayer Ceramic Capacitor and Dielectric Ceramic
Composition)
[0046] FIG. 1 is a partially cut-away perspective view
schematically showing an example of a multilayer ceramic capacitor
of the present invention. FIG. 2 is a sectional view schematically
showing the basic structure of a multilayer ceramic capacitor of
the present invention.
[0047] As shown in FIGS. 1 and 2, a multilayer ceramic capacitor of
the present invention comprises a laminate (referred to as a
"multilayer dielectric device body 10" or a "device body 10"
hereinafter) produced by alternately stacking dielectric layers 2
and internal electrode layers 3. Also, a pair of external
electrodes 4 is formed on both ends of the multilayer dielectric
device body 10 so that the external electrodes 4 are electrically
connected to the respective internal electrode layers 3 alternately
disposed in the device body 10. The shape of the multilayer
dielectric device body 10 is generally a rectangular prism, but it
is not particularly limited. The dimensions are also not
particularly limited, but the dimensions generally include a long
side of about 0.6 to 5.6 mm, a short side of 0.3 to 5.0 mm, and a
height of 0.3 to 1.9 mm.
[0048] The dielectric layers 2 are made of a dielectric ceramic
composition comprising the basic components below. The dielectric
ceramic composition comprises the basic components including (a)
barium titanate, (b) a first sub-component comprising at least one
oxide selected from a Mg oxide, a Ca oxide, a Ba oxide, and Sr
oxide, (c) a second sub-component comprising an oxide containing 1
mol of Si atoms per mol, (d) a third sub-component comprising at
least one selected from a V oxide, a Mo oxide, and a W oxide, (e) a
fourth sub-component comprising at least one R.sup.1 oxide (wherein
R.sup.1 is at least one selected from Sc, Er, Tm, Yb, and Lu), (f)
a fifth sub-component comprising at least one R.sup.2 oxide
(wherein R.sup.2 is at least one selected from Y, Dy, Ho, Tb, Gd,
and Eu), (g) a sixth sub-component comprising at least one selected
from a Mn oxide and a Cr oxide, and (h) a seventh sub-component
comprising at least one selected from calcium zirconate, and a
mixture of a Ca oxide and Zr oxide.
[0049] The ratio of each component of the dielectric ceramic
composition can be expressed by a number of moles relative to 100
moles of barium titanate.
[0050] For example, the dielectric ceramic composition contains the
components in respective number of moles relative to 100 moles of
barium titanate, the components including the first sub-component
comprising a Mg oxide, a Ca oxide, a Ba oxide, or Sr oxide with a
number of moles of 0 to 7 in terms of MgO, CaO, BaO, or SrO, the
second sub-component with a number of moles of 0.5 to 12 in terms
of the oxide containing 1 mol of Si atoms per mol, the third
sub-component comprising a V oxide, a Mo oxide, or a W oxide with a
number of moles of 0.01 to 0.5 in terms of V.sub.2O.sub.5,
MoO.sub.3, or WO.sub.3, the fourth sub-component comprising a
R.sup.1 oxide (wherein R.sup.1 is at least one selected from Sc,
Er, Tm, Yb, and Lu) with a number of moles of 0 to 7 in terms of
R.sup.1.sub.2O.sub.3, the fifth sub-component comprising a R.sup.2
oxide (wherein R.sup.2 is at least one selected from Y, Dy, Ho, Tb,
Gd, and Eu) with a number of moles of 0.5 to 9 in terms of
R.sup.2.sub.2O.sub.3, the sixth sub-component comprising a Mn oxide
or a Cr oxide with a number of moles of 0 to 0.5 in terms of MnO or
Cr.sub.2O.sub.3, and the seventh sub-component comprising calcium
zirconate or a mixture of a Ca oxide and Zr oxide with a number of
moles of 0 to 5 in terms of CaZrO.sub.2 or CaO+ZrO.sub.3.
[0051] In the present invention, barium titanate may deviate from
the stoichiometric composition. In this case, the number of moles
of each component is expressed relative to 100 moles of barium
titanate deviating from the stoichiometric composition. Also, the
oxide as each of the sub-components in the dielectric ceramic
composition may deviate the stoichiometric composition. In this
case, the number of moles of each oxide deviating from the
stoichiometric composition is a number of moles in terms of the
stoichiometric composition relative to 100 moles of barium
titanate. The number of moles of each component is determined based
on quantitative data of atoms of each component. The quantitative
data can be obtained by various conventional known methods. For
example, the quantitative data can relatively easily be obtained by
analysis such as fluorescent X-ray analysis, ICP (radio-frequency
inductively coupled plasma spectroscopy), or the like.
[0052] The reason for limiting the content of each of the
sub-components is as follows:
[0053] When the content of the first sub-component is 0 mole (not
contained), a rate of change in capacitance with temperature is
increased. On the other hand, when the content of the first
sub-component exceeds 7 moles, sinterability degrades. The ratio of
oxides in the first sub-component is any desired value, and the
lower limit of the content of the first sub-component is, for
example, 0.01 mole.
[0054] The second sub-component functions as a sintering aid for
preventing half-baking and, for example, contains silicon oxide as
a main component. When the content of the second sub-component is
less than 0.5 mole, the capacitance-temperature characteristics
degrade, and insulation resistance (IR) decreases. On the other
hand, the content of the second sub-component exceeds 12 moles, the
IR lifetime is insufficient, and the dielectric constant rapidly
decreases. The second sub-component preferably comprises a compound
oxide containing at least one selected from SiO.sub.2, MO (wherein
M is at least one element selected from Ba, Ca, Sr, and Mg),
LiO.sub.2, and B.sub.2O.sub.3. The second sub-component mainly
functions as the sintering aid, but has the effect of improving the
defective ratio of the initial insulation resistance in the form of
a thin layer.
[0055] The compound oxide as the second sub-component is more
preferably represented by (Ba, Ca).sub.xSiO.sub.2+x (x=0.7 to 1.2).
Although Ba and Ca atoms in (Ba, Ca).sub.xSiO.sub.2+x are contained
in the first sub-component, the compound oxide (Ba,
Ca).sub.xSiO.sub.2+x desirably functions as the sintering aid
having high reactivity to the main component because of its low
melting point. In (Ba, Ca).sub.xSiO.sub.2+x, x is in a range of 0.7
to 1.2, and preferably 0.8 to 1.1. When x is less than 0.7, i.e.,
when the content of the Si component is excessively high relative
to the (Ba, Ca) component, the second sub-component reacts with
BaTiO.sub.3 as the main component to worsen the dielectric
characteristics. When x exceeds 1.2, the melting point increases to
undesirably worsen the sinterability. The Ba--Ca ratio may be any
value, and either of Ba and Ca may be contained. In the invention,
the term "IR lifetime" means the time to a decrease in the
insulation resistance of the capacitor to {fraction (1/10)} of the
value at the start of measurement.
[0056] The third sub-component has the effect of flattening the
capacitance-temperature characteristics at temperatures higher than
the Curie temperature of the resultant dielectric ceramic
composition, and the effect of improving the IR lifetime. When the
content of the third sub-component is less than 0.01 mole, these
effects are insufficient. On the other hand, when the content of
the third sub-component exceeds 0.5 mole, IR significantly
decreases. The ratio of oxides in the third sub-component is any
desired value.
[0057] The fourth sub-component functions as a donor (donor for
preventing movement of oxygen defects) for preventing insulation
breakdown of a dielectric material due to movement of oxygen
defects with the electric field applied. The fourth sub-component
need not be necessarily added, and the amount of the fourth
sub-component added may be 0 mole. However, the time to insulation
breakdown can be increased by adding the fourth sub-component and
increasing the adding amount thereof. The fourth sub-component also
has the effect of shifting the Curie temperature of the resulting
dielectric ceramic composition to the higher temperature side, and
the effect of flattening the capacitance-temperature
characteristics. When the content of the fourth sub-component
exceeds 7 moles, half-baking may occur to in turn decrease the
lifetime. As the fourth sub-component, an Yb oxide is preferred
because of its high effect of improving characteristics and low
cost.
[0058] Like the fourth sub-component, the fifth sub-component
functions as a donor (donor for preventing movement of oxygen
defects) for preventing insulation breakdown of a dielectric
material due to movement of oxygen defects with the electric field
applied. The fifth sub-component need not be necessarily added, and
the amount of the fourth sub-component added may be 0 mole.
However, the time to insulation breakdown can be increased by
adding the fifth sub-component. The fourth sub-component also has
the effect of improving IR and IR lifetime, and has a small adverse
effect on the capacitance-temperature characteristics. When the
content of the fifth sub-component is less than 0.5 mole, the time
to insulation breakdown cannot be increased. On the other hand,
when the content of the fifth sub-component exceeds 9 moles,
half-baking may occur to in turn decrease the lifetime. As the
fifth sub-component, a Y oxide is preferred because of low cost and
its large effect of improving characteristics.
[0059] The sixth sub-component has the effect of promoting
sintering, the effect of increasing IR, and the effect of improving
IR lifetime. In order to sufficiently obtain these effects, the
ratio of the sixth sub-component relative to 100 moles of
BaTiO.sub.3 is preferably 0 (preferable lower limit 0.01 mole) to
0.5 mole. When the content of the sixth sub-component exceeds 0.5
mole, the capacitance-temperature characteristics may be adversely
affected.
[0060] The seventh sub-component has the effect of shifting the
Curie temperature of the resulting dielectric ceramic composition
to the higher temperature side, and the effect of flattening the
capacitance-temperature characteristics. When the content of the
seventh sub-component exceeds 5 moles, the IR accelerated lifetime
significantly decreases, and the capacitance-temperature
characteristics (X8R characteristic) worsen. Although the form of
calcium zirconate (for example, represented by CaZrO.sub.3)
contained as the seventh sub-component is not particularly limited,
for example, it is contained as a compound oxide such s CaZrO.sub.3
or the like. The seventh sub-component is contained using a Ca
oxide such as CaO, a carbonate such as CaCO.sub.3, an organic
compound, CaZrO.sub.3, or the like as a raw material. The Ca--Zr
ratio in terms of CaZrO.sub.3 or CaO+ZrO.sub.2 is not particularly
limited, and may be determined so that the seventh component is not
dissolved in BaTiO.sub.3 as the main component. The molar ratio
(Ca/Zr) of Ca to Zr is preferably 0.5 to 1.5, more preferably 0.8
to 1.5, and most preferably 0.9 to 1.1. The term "IR accelerated
lifetime" means the time to a decrease in insulation resistance of
the capacitor to {fraction (1/10)} of the value at the start of
measurement in an acceleration test at 200.degree. C. in an
electric field of 15 V/.mu.m.
[0061] In the dielectric ceramic composition, the contents of the
fourth sub-component (R.sup.1 oxide, i.e., rare earth element
oxide) and the seventh sub-component (CaZrO.sub.3 or CaO+ZrO.sub.2)
are controlled to flatten the capacitance-temperature
characteristics (X8R characteristic) and improve the
high-temperature accelerated lifetime. In particular, within the
above-described numerical ranges, precipitation of a heterogenous
phase is suppressed, thereby homogenizing the texture.
[0062] The dielectric ceramic composition may further contain an Al
oxide (for example, Al.sub.2O.sub.3) besides the above-described
oxides. An Al oxide exhibits the effect of improving sinterability
and the IR and IR lifetime with little influence on the
capacitance-temperature characteristics.
[0063] The dielectric ceramic composition containing the basic
components at the above-described component ratios according to the
present invention is characterized in that the ratio (A/B) of the
number of moles A of the second sub-component to the total number
of moles B of the fourth and fifth sub-components is 0.7 or more
(referred to as "dielectric ceramic composition I" in the
invention). The dielectric ceramic composition I having an A/B
ratio of 0.7 or more satisfies the X8R characteristic and has a
long mean time to failure. When the A/B ratio is less than 0.7, a
dielectric ceramic composition having a long mean time to failure
cannot be obtained.
[0064] In a conventional barium titanate-based dielectric ceramic
composition, when an electric field is applied, oxygen defects
present in a dielectric material move to break down the insulation
of the dielectric material. Therefore, rare earth elements (R.sup.1
atoms and R.sup.2 atoms) functioning as a donor are added for
preventing the movement of the oxygen defects. Although the
addition of the rare earth element increases the time to breakdown
of insulation, the addition of a large amount of rare earth
elements may cause half-baking and may in turn decrease the
lifetime. In the present invention, in order to prevent this
problem, the ratio of the second sub-component functioning as a
sintering aid for preventing half-baking to the total of the fourth
and fifth sub-components comprising rare earth elements functioning
as a donor is controlled in the above-described range, thereby
producing the dielectric ceramic composition 1 having a long mean
time to failure.
[0065] As described above, the number of moles A of the second
sub-component is converted into the number of moles of the oxide
containing 1 mole of Si atoms per mole. For example, when the
second sub-component is a compound oxide represented by (Ba,
Ca).sub.xSiO.sub.2+x (x=0.7 to 1.2), the number of moles A is the
number of moles of the Si atoms in the compound oxide.
[0066] The total number of moles B of the fourth sub-component
(rare earth oxide: R.sup.1 oxide) and the fifth sub-component (rare
earth oxide: R.sup.2 oxide) is preferably 8 moles or less, and more
preferably 6.5 moles or less, relative to 100 moles of BaTiO.sub.3.
When the total number of moles B is 5 or less, the sinterability
can be kept higher.
[0067] The dielectric ceramic composition having the basic
components at the above-described component ratios according to the
present invention is also characterized in that the ratio (C/D) of
the number of moles C of Si atoms in the second sub-component to
the total number of moles D of the atoms in the first to seventh
sub-components excluding Si atoms and oxygen atoms is 0.2 or more,
and the total number of moles of the fourth and fifth sub-component
is 3 or more (referred to as "dielectric ceramic composition II" in
the invention).
[0068] The dielectric ceramic composition II having a C/D ratio of
0.2 or more and a total number of moles of the fourth and fifth
sub-components of 3 or more has a long mean time to failure (MTTF)
and excellent reliability. This is possibly because the fourth and
fifth sub-components function as donor components for preventing
the movement of oxygen defects, and the amount of Si functioning as
a grain boundary component is increased by setting the C/D ratio to
0.2 or more, thereby increasing the electric field applied to the
grain boundaries and eliminating the electric field applied to the
insides of grains. When the C/D ratio is less than 0.2 or the total
number of moles of the fourth and fifth sub-components is less than
3, the resulting dielectric ceramic composition cannot satisfy the
desired mean time to failure.
[0069] Since the second sub-component comprises an oxide containing
1 mole of Si atoms per mole, the number of moles C of Si atoms in
the second sub-component is the same as that of the oxide added as
the second sub-component. On the other hand, "oxygen atoms" means
the oxygen constituting the dielectric ceramic composition.
Therefore, the total number of moles D of the atoms in the first to
seventh sub-component excluding the Si atoms and oxygen atoms
contained in the dielectric ceramic composition is the total number
of moles of the atoms excluding Ba atoms and Ti atoms in
BaTiO.sub.3 as the main component, Si atoms in the second
sub-component, and all oxygen atoms in the dielectric ceramic
composition. The total number of moles D can be determined by
quantitative analysis of the elements contained in the dielectric
ceramic composition using measurement means such as fluorescent
X-ray analysis, ICP (radio-frequency inductively coupled plasma
spectroscopy), or the like. For example, the components (Ba, Ti,
Mg, Ca, Sr, Si, V, Mo, W, Sc, Er, Tm, Yb, Lu, Y, Dy, Ho, Tb, Gd,
Eu, Mn, Cr, Zr, and the like) other than oxygen atoms in the
dielectric ceramic composition are quantitatively analyzed to
calculate the number of moles of each element. The number of moles
of Ba atoms added as a sub-component is calculated by subtracting a
number of moles of Ba in terms of the stoichiometric composition of
BaTiO.sub.3 from a number of moles of Ba calculated based on the
number of moles of Ti atoms. With respect to the other components,
the number of moles of each element is calculated as a number of
moles of atoms in each sub-component. The C/D ratio can be
calculated from the calculated number of moles of each of the
components. The number of moles of the fourth and fifth
sub-components are calculated based on the result of quantitative
analysis of the rare earth elements including Sc, Er, Tm, Yb, Lu,
Y, Dy, Ho, Tb, Gd, and Eu.
[0070] When the dielectric ceramic composition has a C/D ratio of
0.2 or more and less than 0.24, there is the effect of decreasing a
variation in the mean time to failure in addition to the effect of
improving the mean time to failure (MTTF). Although the reason for
this is not known, a conceivable reason is that the amount of Si
functioning as the grain boundary component is optimized. The
variation in lifetime is shown by an m value which indicates the
inclination of a regression line in a Weibull distribution. As the
m value increases, the variation in the mean time to failure (MTTF)
decreases, and reliability becomes excellent. When the C/D ratio is
less than 0.20 and 0.24 or more, the variation in the mean time to
failure tends to increase (the m value tends to decrease), and
satisfactory reliability cannot be obtained.
[0071] The Curie temperature (temperature of phase transition from
ferroelectric to dielectric) of the dielectric ceramic composition
(including both the dielectric ceramic compositions I and II
hereinafter) can be changed by changing the composition of the
dielectric ceramic composition. However, in order to satisfy the
X8R characteristic, the Curie temperature is preferably 120.degree.
C. or more, and more preferably 123.degree. C. or more. The Curie
temperature can be measured by DSC (differential scanning
calorimetry) or the like. When Ba or Ti of the main component
having a perovskite structure is substituted by at least one of Sr,
Zr, and Sn, the Curie temperature is shifted to the lower
temperature side, thereby deteriorating the capacitance-temperature
characteristics. Therefore, it is preferable that BaTiO.sub.3 [for
example, (Ba, Sr)TiO.sub.3] containing such elements is not used as
the main component. However, there is no problem as long as the
content of at least one of Sr, Zr, and Sn is an impurity level (for
example, about 0.1 mol % or less of the whole of the dielectric
ceramic composition).
[0072] The dielectric particles constitute a dielectric layer
formed by firing the dielectric ceramic composition. However, in
the present invention, the average particle diameter of the
dielectric particles is not particularly limited, and may be
appropriately determined in a range of, for example, 0.1 to 3
.mu.m, according to the thickness of the dielectric layer, and the
like. More specifically, when the average particle diameter is 0.1
to 0.5 .mu.m, the IR lifetime is effectively increased, and changes
in capacitance with time under a DC electric field can be
decreased. In the present invention, the average particle diameter
of the dielectric particles is determined by a code method.
[0073] The sentence "the capacitance-temperature characteristics
satisfy the X8R characteristic stipulated in the EIA standard"
means that the produced multilayer ceramic capacitor can be
preferably used as an electronic part for an apparatus used in an
environment of 80.degree. C. or more, particularly 125.degree. C.
to 150.degree. C. In this temperature range, the
capacitance-temperature characteristics satisfy the R
characteristic stipulated in the EIA standard and further satisfy
the X8R characteristic (.DELTA.C/C=.+-.15% at -55.degree. C. to
150.degree. C.) stipulated in the EIA standard. Also, the
temperature characteristics can simultaneously satisfy the B
characteristic [rate of change in capacitance is .+-.15% (reference
temperature 20.degree. C.) at -25.degree. C. to 85.degree. C.]
stipulated in the EIA standard and the X7R characteristic
(.DELTA.C=.+-.15% at -55.degree. C. to 125.degree. C.) stipulated
in the EIA standard. The phrase "excellent change in capacitance
with time" means that a rate of change in capacitance is less than
10% 1000 hours after when a DC voltage of, for example, 7 V/.mu.m
is applied to the produced multilayer ceramic capacitor at a
temperature of, for example, 85.degree. C.
[0074] Although the number and the thickness of the dielectric
layers 2 stacked may be appropriately determined according to
purposes and applications, the thickness of the dielectric layers 2
is generally 30 .mu.m or less. From the viewpoint of decreasing the
size and increasing the capacitance, the thickness of the
dielectric layers 2 is preferably 10 .mu.m or less. The multilayer
ceramic capacitor comprising such thin dielectric layers permits
the realization of a smaller size and higher capacitance, and the
average particle diameter of the dielectric particles constituting
the dielectric layers is specified to effectively improve the
capacitance-temperature characteristics. The lower limit of the
thickness of the dielectric layers is not particularly limited.
However, if an example is to be quoted, the lower limit is about
0.5 .mu.m. The number of the dielectric layers stacked is generally
about 2 to 1000.
[0075] The dielectric layers 2 and internal electrode layers 3 are
alternately provided, and the ends of these layers 2 and 3 are
alternately exposed from the two opposite end surfaces of the
multilayer dielectric device body 10. Also, a pair of external
electrodes 4 is formed on both ends of the multilayer dielectric
device body 10 and connected to the exposed ends of the nickel
internal electrode layers 3 disposed alternately to form the
multilayer ceramic capacitor.
[0076] The internal electrode layers 3 comprise a non-metallic
conductive material substantially functioning as electrodes.
Specifically, Ni or a Ni alloy is preferred. As the Ni alloy, a Ni
alloy with at least one of Mn, Cr, Co, Al, W, and the like is
preferred, and the Ni content of the alloy is preferably 95% by
weight or more. Ni or the Ni alloy may contain 0.1% by weight or
less of trace components such as P, C, Nb, Fe, Cl, B, Li, Na, K, F,
S, and the like. The number and thickness of the internal electrode
layers 3 stacked may be appropriately determined according to
purposes and application. With the dielectric ceramic composition
I, the thickness of the internal electrode layers 3 is preferably
about 0.1.mu. to 5 .mu.m, and more preferably 0.5 .mu.m to 2.5
.mu.m. With the dielectric ceramic composition II, the thickness of
the internal electrode layers 3 is preferably about 0.5.mu. to 10
.mu.m, and more preferably 1 .mu.m to 2.5 .mu.m.
[0077] The external electrodes 4 are electrically connected to the
internal electrode layers 3 alternately disposed in the multilayer
ceramic device body 10, and formed at both ends of the multilayer
ceramic device body 10. In general, at least one of Ni, Pd, Ag, Au,
Cu, Pt, Rh, Ru, Ir, and the like or an alloy thereof can be used
for the external electrodes 4. Specifically, Cu, a Cu alloy, Ni, a
Ni alloy, Ag, an Ag--Pd alloy, an In--Ga alloy, or the like can be
used. Although the thickness of the external electrodes 4 may be
appropriately determined according to applications, the thickness
is preferably about 10 .mu.m to 200 .mu.m.
[0078] (Method for Manufacturing Multilayer Ceramic Capacitor)
[0079] Like a conventional multilayer ceramic capacitor, the
multilayer ceramic capacitor of the present invention is
manufactured by forming a green chip by a usual printing method or
sheet method using a paste, firing the green chip, forming external
electrodes by printing or transfer, and then firing the external
electrodes.
[0080] More specifically, the multilayer ceramic capacitor is
manufactured by a method comprising a step of preparing the
above-described dielectric ceramic composition raw material; a step
of alternately stacking green sheets for forming the dielectric
layers and paste layers for forming the internal electrode layers
to form a laminate, the green sheets being formed using a paste for
the dielectric layers containing the dielectric ceramic composition
raw material, and the base layers being formed using a paste for
the internal electrodes; and a step of firing the laminate to form
a ceramic chip in which the green sheets become the dielectric
layers and the base layers become the internal electrode layers;
and a step of reoxidizing the dielectric layers in the ceramic
chip. The manufacturing method will be described in detail
below.
[0081] The paste for the dielectric layers comprises a coating
material produced by kneading the dielectric ceramic composition
raw material and an organic vehicle, and the coating material may
be either an organic or aqueous coating material.
[0082] As the dielectric ceramic composition raw material, the
above oxides, a mixture thereof, or a compound oxide can be used.
However, compounds can be appropriately selected from various
compounds which converted to the oxides or the compound oxide by
firing, for example, carbonates, oxalates, nitrates, hydroxides,
and organic metal compounds, and mixed. In the dielectric ceramic
composition raw material, the content of each of the oxides and/or
a compound converted to each oxide by firing may be determined so
that the above-described dielectric ceramic composition can be
obtained after firing. The dielectric ceramic composition raw
material generally comprises a powder having an average particle
diameter of about 0.1 .mu.m to 3 .mu.m.
[0083] In more detail, the dielectric ceramic composition raw
material comprises basic components including (1) barium titanate
and/or a compound or a mixture converted to barium titanate by
firing, (2) a first sub-component comprising at least one oxide
selected from MgO, CaO, BaO, and SrO and/or a compound converted to
the oxide by firing, (3) a second sub-component comprising an oxide
containing 1 mol of Si atoms per mol, (4) a third sub-component
comprising at least one oxide selected from V.sub.2O.sub.5,
MoO.sub.3, WO.sub.3 and/or a compound converted to the oxide by
firing, (5) a fourth sub-component comprising at least one oxide
represented by R.sup.1.sub.2O.sub.3 (wherein R.sup.1 is an element
selected from Sc, Er, Tm, Yb, and Lu) and/or a compound converted
to the oxide by firing, (6) a fifth sub-component comprising at
least one oxide represented by R.sup.2.sub.2O.sub.3 (wherein
R.sup.2 is at least one selected from Y, Dy, Ho, Tb, Gd, and Eu)
and/or a compound converted to the oxide by firing, (7) a sixth
sub-component comprising at least one oxide selected from MnO and
Cr.sub.2O.sub.3 and/or a compound converted to the oxide by firing,
and (8) a seventh sub-component comprising at least one compound
selected from CaZrO.sub.3, a mixture of CaO and ZrO.sub.2, a
compound converted to CaZrO.sub.3 by firing, and a mixture of
compounds converted to CaO and ZrO.sub.2, respectively, by firing,
the numbers of moles of the first, second, third, fourth, fifth,
sixth, and seventh sub-components relative to 100 moles of the
barium titanate being 0 to 7, 0.5 to 12, 0.01 to 0.5, 0 to 7, 0.5
to 9, 0 to 0.5, and 0 to 5, respectively, in terms of the
respective oxides.
[0084] As the dielectric ceramic composition raw material
comprising the above basic components, a dielectric ceramic
composition raw material I in which the ratio (A/B) of the number
of moles A of the second sub-component to the total number of moles
B of the fourth and fifth sub-components is 0.7 or more is used for
the dielectric ceramic composition I.
[0085] On the other hand, as the dielectric ceramic composition raw
material comprising the above basic components, a dielectric
ceramic composition raw material II in which the ratio (C/D) of the
number of moles A of Si atoms in the second sub-component to the
total number of moles D of atoms in the first to seventh
sub-components excluding Si atoms and oxygen atoms in the
dielectric ceramic composition is 0.2 or more, and the total number
of moles of the fourth and fifth sub-components 3 moles or more is
used for the dielectric ceramic composition II.
[0086] The organic vehicle is produced by dissolving a binder in an
organic solvent. The binder used for the organic vehicle is not
particularly limited, and the binder may be appropriately selected
from usual binders such as ethyl cellulose, and polyvinyl butyral.
The organic solvent used is not particularly limited, and the
solvent may be appropriately selected from various organic solvents
such as terpineol, butyl carbitol, acetone, and toluene according
to the method used, such as the printing method or the sheet
method.
[0087] When the paste for the dielectric layers comprises an
aqueous coating material, an aqueous vehicle containing a
water-soluble binder and a dispersant which are dissolved in water
and the dielectric ceramic composition raw material may be kneaded.
The water-soluble binder used in the aqueous vehicle is not
particularly limited, and for example, polyvinyl alcohol,
cellulose, water-soluble acrylic resin, or the like may be
used.
[0088] The paste for the internal electrode layers is prepared by
kneading a conductive material comprising the above-described
dielectric metal or alloy or an oxide converted to the conductive
material after firing, an organic metal compound, resinate, and the
organic vehicle. The paste for the external electrodes may be
prepared by the same method as that for the paste for the internal
electrode layers.
[0089] The content of the organic vehicle in each paste is not
particularly limited, and the vehicle generally contains about 1 to
5% by weight of the binder and 10 to 50% by weight of the solvent.
Each paste may further contain additives selected from various
dispersants, plasticizers, dielectrics, insulators, and the like.
The total content of the additives is preferably 10% by weight or
less.
[0090] In use of the printing method, the paste for the dielectric
layers and the paste for the internal electrode layers are
alternately stacked on a PET substrate or the like to form a
laminate, and the laminate is then cut into a predetermined shape
and then separated from the substrate to form a green chip. In use
of the sheet method, a green sheet is formed using the paste for
the dielectric layers, and the paste for the internal electrode
layers is printed on the green sheet, and then a plurality of green
sheets is stacked to form a green chip.
[0091] The green chip is subjected to removal of the binder before
firing. The removal of the binder may be performed under usual
conditions. However, when a base metal such as Ni or an Ni alloy is
used as the conductive material of the internal electrode layers,
the heating rate in an air atmosphere is preferably 5 to
300.degree. C./hr and more preferably 10 to 100.degree. C./hr, the
retention temperature is preferably 180.degree. C. to 400.degree.
C., and more preferably 200.degree. C. to 300.degree. C., and the
temperature retention time is preferably 0.5 to 24 hours and more
preferably 5 to 20 hours.
[0092] The atmosphere for firing the green chip may be
appropriately determined according to the type of the conductive
material in the paste for the internal electrode layers. However,
when a base metal such as Ni or a Ni alloy is used as the
conductive material, the oxygen partial pressure in the firing
atmosphere is preferably 10.sup.-8 atm to 10.sup.-12 atm. When the
oxygen partial pressure is less than this range, the conductive
material of the internal electrode layers is abnormally sintered to
cause discontinuity. If the oxygen partial pressure exceeds the
above range, the internal electrode layers tend to be oxidized.
[0093] During firing, the retention temperature is preferably
1100.degree. C. to 1400.degree. C., more preferably 1200.degree. C.
to 1360.degree. C., and most preferably 1200.degree. C. to
1320.degree. C. When the retention temperature is less than the
range, densification becomes insufficient, while when the retention
temperature exceeds the range, discontinuity of the electrodes
occurs due to abnormal sintering of the internal electrode layers,
the capacitance-temperature characteristics deteriorate due to
diffusion of the internal electrode component materials, and the
dielectric ceramic composition is easily reduced.
[0094] As the other firing conditions, the heating rate is
preferably 50 to 500.degree. C./hr, and more preferably 200 to
300.degree. C./hr, the temperature retention time is preferably 0.5
to 8 hours and more preferably 1 to 3 hours, and the cooling rate
is preferably 50 to 500.degree. C./hr and more preferably 200 to
300.degree. C./hr. The firing atmosphere is preferably a reducing
atmosphere, and, for example, a mixed gas of N.sub.2 and H.sub.2 is
preferably humidified and used as the atmospheric gas.
[0095] When firing is performed in the reducing atmosphere, the
multilayer dielectric device body is preferably annealed. Annealing
is performed for re-oxidizing the dielectric layers, thereby
increasing the IR lifetime and improving reliability.
[0096] The oxygen partial pressure in the annealing atmosphere is
10.sup.-6 atm or more, particularly 10.sup.-5 to 10.sup.-4 atm.
When the oxygen partial pressure is less than the above range,
re-oxidation of the dielectric layers becomes difficult. When the
oxygen partial pressure exceeds the above range, the internal
electrode layers tend to be oxidized.
[0097] During annealing, the retention temperature is preferably
1100.degree. C. or less, particularly 500.degree. C. to
1100.degree. C. When the retention temperature is less than the
above range, oxidation of the dielectric layers becomes
insufficient. Therefore, the IR tends to decrease, and the IR
lifetime tends to decrease. On the other hand, when the retention
temperature exceeds the above range, the internal electrode layers
are oxidized to decrease the capacitance, and the internal
electrode layers react with the dielectric base material to easily
degrade the capacitance-temperature characteristics and decrease
the IR and the IR lifetime. The annealing may comprise only a
heating step and a cooling step. Namely, the temperature retention
time may be zero. In this case, the retention temperature
corresponds to the highest temperature.
[0098] As other annealing conditions, the temperature retention
time is preferably 0 to 20 hours and more preferably 6 to 10 hours,
and the cooling rate is preferably 50 to 500.degree. C./hr and more
preferably 100 to 300.degree. C./hr. As the annealing atmospheric
gas, for example, wet N.sub.2 gas is preferably used.
[0099] In the removal of the binder, firing, and annealing, the
N.sub.2 gas and the mixed gas are humidified by, for example, a
wetter or the like. In this case, the water temperature is
preferably about 5.degree. C. to 75.degree. C.
[0100] The removal of the binder, firing, and annealing may be
performed continuously or independently. When these treatments are
continuously performed, preferably, the atmosphere is changed
without cooling after the removal of the binder, and then the
temperature is increased to the retention temperature for firing.
Then, the temperature is decreased by cooling to the retention
temperature for annealing, and the atmosphere is changed to perform
annealing. On the other hand, the treatments are independently
performed, preferably, the temperature is increased to the
retention temperature for the removal of the binder in a N.sub.2
gas or wet N.sub.2 gas atmosphere, and then the atmosphere is
changed. Then, the temperature is further increased for firing. For
annealing, the temperature is decreased by cooling to the retention
temperature for annealing, and then the atmosphere is changed to
the N2 gas or wet N2 gas atmosphere. Then, cooling is further
continued for annealing. For annealing, the atmosphere may be
changed after the temperature is increased to the retention
temperature in the N.sub.2 gas atmosphere, and the whole step may
be performed in the wet N.sub.2 gas atmosphere.
[0101] The ends of the multilayer dielectric device body obtained
as described above are polished by, for example, barrel polishing,
sand blasting, or the like, and the paste for the external
electrodes is printed or transferred and then fired to form the
external electrodes 4. For example, the paste for the external
electrodes is preferably fired in a wet mixed gas of N.sub.2 and
H.sub.2 at 600.degree. C. to 800.degree. C. for about 10 minutes to
1 hour. If required, coating layers are formed on the surfaces of
the external electrodes 4 by plating or the like. The multilayer
ceramic capacitor of the present invention is mounted on a printed
circuit board by soldering or the like and used for various
electronic apparatuses.
[0102] The multilayer ceramic capacitor of the present invention
and the manufacturing method therefore are described above.
However, the present invention is not limited to this, and of
course, the present invention can be carried out in various modes
within the scope of the gist.
EXAMPLES
[0103] The present invention will be described in detail below with
reference to examples and comparative examples. However, the
present invention is not limited to the description below.
[0104] (Preparation of Sample 1)
[0105] First, a main component raw material (BaTiO.sub.3) and first
to seventh sub-component raw materials having an average particle
diameter of 0.1 to 1 .mu.m were prepared as starting materials for
producing a dielectric material. With respect to BaTiO.sub.3 as the
main component, BaCO.sub.3 and TiO.sub.2 were weighed and wet-mixed
with a ball mill for about 16 hours. Then, the resultant mixture
was dried, fired in air at a temperature of about 1100.degree. C.,
and then further wet-ground with a ball mill for about 16 hours to
produce BaTiO.sub.3 similar to the prepared raw material
BaTiO.sub.3. Also, similar BaTiO.sub.3 used as the main component
could be produced by hydrothermal synthesis, oxalate method, or the
like.
[0106] Carbonates (first sub-component: MgCO.sub.3, sixth
sub-component: MnCO.sub.3) were used as raw materials for MgO and
MnO, respectively, and oxides (second sub-component:
(Ba.sub.0.6Ca.sub.0.4)SiO.sub.3, third sub-component:
V.sub.2O.sub.5, fourth sub-component: Yb.sub.2O.sub.3, fifth
sub-component: Y.sub.2O.sub.3, seventh sub-component: CaZrO.sub.3)
were used as the other raw materials. These sub-components were
prepared so that the number of moles of each sub-component in terms
of the oxide relative to 100 moles of BaTiO.sub.3 was as shown in
Table 1. The sub-components were wet-mixed by a ball mill for 16
hours and then dried to prepare a dielectric ceramic composition
raw material 1. In order to produce the second sub-component
(Ba.sub.0.6Ca.sub.0.4)SiO.sub.3, BaCO.sub.3, CaCO.sub.3, and
SiO.sub.2 were wet-mixed by a ball mill for 16 hours, dried, fired
in air at 1150.degree. C., and then further wet-ground by a ball
mill for 100 hours. The seventh sub-component CaZrO.sub.3 was
produced by wet-mixing CaCO.sub.3 and ZrO.sub.2 by a ball mill for
16 hours, drying and then firing the resulting mixture in air at
1150.degree. C., and then wet-grinding the mixture by a ball mill
for 24 hours.
[0107] Then, 100 parts by weight of the dry dielectric ceramic
composition raw material prepared as described above, 4.8 parts by
weight of an acrylic resin, 40 parts by weight of methylene
chloride, 20 parts by weight of ethyl acetate, 6 parts by weight of
mineral spirit, and 4 parts by weight of acetone were mixed by a
ball mill to form a paste for dielectric layers.
[0108] Then, 100 parts by weight of Ni particles having an average
particle diameter of 0.4 .mu.m, 40 parts by weight of an organic
vehicle (prepared by dissolving 8 parts by weight of ethyl
cellulose in 92 parts by weight of butyl carbitol), and 10 parts by
weight of butyl carbitol were kneaded by three rolls to form a
paste for internal electrode layers. For external electrodes, a
paste-like In--Ga alloy was prepared.
[0109] Next, a green sheet of 4.5 .mu.m in thickness was formed on
a PET film using the paste for dielectric layers, and the paste for
internal electrode layers was printed on the green sheet. Then, the
green sheet was separated from the PET film, and the green sheet
and a protective green sheet (without the paste for internal
electrode layers printed thereon) were stacked and compressed to
form a green chip. The number of the sheets having the internal
electrodes stacked was 5.
[0110] Next, the green chip was cut into a predetermined size,
subjected to removal of the binder, fired and then annealed to
produce a sintered compact used as a multilayer ceramic chip. The
removal of the binder was performed in an air atmosphere under the
conditions including a heating rate of 32.5.degree. C./hr, a
retention temperature of 260.degree. C., and a retention time of 8
hours. Firing was performed in an atmosphere of a wet
N.sub.2+H.sub.2 gas mixture (oxygen partial pressure: 10.sup.-12
atm) under the conditions including a heating rate of 200.degree.
C./hr, a retention temperature of 1320.degree. C., a retention time
of 2 hours, and a cooling rate of 200.degree. C./hr. Annealing was
performed in an atmosphere of a wet N.sub.2 gas (oxygen partial
pressure: 10.sup.-5 atm) under the conditions including a retention
temperature of 1050.degree. C., a temperature retention time of 2
hours, and a cooling rate of 200.degree. C./hr. The atmospheric
gases used for firing and annealing were humidified by a wetter at
a water temperature of 20.degree. C.
[0111] Next, the end surfaces of the multilayer ceramic chip were
polished by sand blasting, and the external electrodes were formed
by coating the paste-like In--Ga alloy on the end surfaces to
prepare Sample 1 of the multilayer ceramic capacitor I. The sample
was of a size of 3.2 mm.times.1.6 mm.times.0.6 mm, the number of
the dielectric layers held between the respective internal
electrode layers was 5, the thickness of each dielectric layer was
3.5 .mu.m, and the thickness of each internal electrode layer was
1.0 .mu.m.
[0112] Sample 1 of the multilayer ceramic capacitor I was not
reduced even by firing in a reducing atmosphere, and nickel used
for the internal electrodes was not oxidized to an extent which
caused IR failure.
[0113] (Preparation of Samples 2 to 17)
[0114] Samples 2 to 17 of the multilayer ceramic capacitor I were
prepared by the same method as that for preparing Sample 1 except
that the composition of the dielectric ceramic composition raw
material I was changed to each of the compositions shown in Table
1.
[0115] Each of the samples of the multilayer ceramic capacitor. I
was not reduced even by firing in a reducing atmosphere, and nickel
used for the internal electrodes was not oxidized to an extent
which caused IR failure.
[0116] (Preparation of Samples 18 to 40)
[0117] Samples 18 to 40 of the multilayer ceramic capacitor II were
prepared by the same method as that for preparing Sample 1 except
that the composition of the dielectric ceramic composition raw
material II was changed to each of the compositions shown in Table
2.
[0118] Each of the samples of the multilayer ceramic capacitor II
was not reduced even by firing in a reducing atmosphere, and nickel
used for the internal electrodes was not oxidized to an extent
which caused IR failure.
[0119] (Preparation of Comparative Sample 1)
[0120] Comparative Sample 1 of the multilayer ceramic capacitor was
prepared by the same method as that for preparing Sample 1 except
that the composition of the dielectric ceramic composition raw
material was changed to that shown in Table 2.
[0121] (Method for Evaluating Characteristics and Results)
[0122] With respect to each of Samples 1 to 17 of the multilayer
ceramic capacitor I, Table 1 shows the ratio (A/B) of the number of
moles A of the second sub-component, which showing the ratio of the
sintering aid added, to the total number of moles B of the fourth
and fifth sub-components, and the results of measurement and
evaluation of MTTF (mean time to failure). In the present
invention, Rank-A (MTTF of 10 hours or more) and Rank-B (MTTF of
less than 10 hours) are used as evaluation critera.
[0123] With respect to each of Samples 1, 18 to 40, and Comparative
Sample 1 of the multilayer ceramic capacitor II, Table 2 shows the
ratio (C/D) of the number of moles C of Si atoms in the second
sub-component to the total number of moles D of the atoms in first
to seventh sub-components excluding Si atoms and oxygen atoms in
the dielectric ceramic composition, and the total number of moles
the fourth and fifth sub-components. Table 2 also shows the results
of measurement and evaluation of MTTF (mean time to failure) and m
value (lifetime variation). In the present invention, include
Rank-A (MTTF of 10 hours or more) and Rank-B (MTTF of less than 10
hours) are used as evaluation criteria for MTTF, and Rank-A (m
value of 2.9 or more) and Rank-B (m value of less than 2.9) are
used as evaluation criteria for the m value.
[0124] The MTTF (mean time to failure) is shown by a mean lifetime
(hour: hr) calculated from a Weibull function on the basis of the
results of a high accelerator life test (HALT) at an atmospheric
temperature of 200.degree. C. with the applied voltage of 15 V/m.
The m value is shown by an inclination of a regression line in a
Weibull distribution.
[0125] The capacitance-temperature characteristics were also
measured. The capacitance-temperature characteristics of each of
the prepared samples were evaluated by measuring a range of change
(%) of capacitance at a temperature of 150.degree. C. at which the
capacitance-temperature characteristics most degrade within the
temperature range of -55.degree. C. to 150.degree. C. The
capacitance was measured by a LCR meter under the conditions of a
frequency of 1 kHz and an input signal level of 1 Vrms. The results
of measurement were evaluated by deciding whether or nor the X8R
characteristic (.DELTA.C/C=.+-.15% at -55.degree. C. to 150.degree.
C.) was satisfied. When the X8R characteristic was satisfied, the
characteristics were evaluated as Rank-A1 and when the X8R
characteristic was not satisfied, the characteristics were
evaluated as Rank-C. The results are shown in Table 1 and 2.
Samples 1 to 17 and 18 to 40 show a rate of change in capacitance
of 15% or less, and it was thus confirmed that the X8R
characteristic is satisfied.
[0126] The results shown in Table 1 indicate that Samples 2 to 9
among Samples 1 to 17 show a MTTF of 10 hours or more and good
results. On the other hand, Samples 10 to 17 show a MTTF of less
than 10 hours.
[0127] The results shown in Table 2 indicate that Samples 20 to 29
having a C/D ratio of 0.2 or more show large MTTF, as compared with
the other samples having a C/D ratio of less than 0.2. Namely, the
samples having a C/D ratio of less than 0.2 show a MTTF or 15 hours
or less, while Samples 20 to 29 having a C/D ratio of 0.2 or more
show a MTTF or 18 hours or more. Therefore, a significant
difference is observed between both types of samples.
[0128] With respect to the m value, Samples 20 to 23, 25, and 27 to
29 among Samples 20 to 29 showing a MTTF of 18 hours or more show
an m value of 2.9 or more. It was thus confirmed that the
multilayer ceramic capacitor II has a small variation in
lifetime.
[0129] As shown in Table 2, Comparative Sample 1 having a total of
the first and fifth sub-components of 2.0 moles shows a MTTF of 4
hours.
1 TABLE 1 Main component (moles) Sub-component (moles)
BCG/(Yb.sub.2O.sub.3 + Y.sub.2O.sub.3) MTTF Sample BaTiO.sub.3
MgCO.sub.3 BCG V.sub.2O.sub.5 Yb.sub.2O.sub.3 Y.sub.2O.sub.3
MnCO.sub.3 CaZrO.sub.3 (Molar ratio) Time Evaluation X8R 1 100 0.90
2.5 0.1 1.75 2.0 0.37 1.5 0.67 8 Rank-B Rank-A 2 100 0.90 3.0 0.1
1.75 2.5 0.37 1.5 0.71 11 Rank-A Rank-A 3 100 0.90 4.0 0.1 1.75 2.5
0.37 1.5 0.94 32 Rank-A Rank-A 4 100 0.50 3.0 0.1 1.00 2.0 0.37 1.0
1.00 30 Rank-A Rank-A 5 100 0.08 4.0 0.1 0 4.5 0.37 1.5 0.89 28
Rank-A Rank-A 6 100 0.08 4.0 0.1 0 5.0 0.37 1.5 0.80 18 Rank-A
Rank-A 7 100 0.08 3.5 0.1 0 4.0 0.37 1.5 0.88 28 Rank-A Rank-A 8
100 0.08 3.5 0.1 0 4.5 0.37 1.5 0.78 19 Rank-A Rank-A 9 100 0.08
3.0 0.1 0 3.5 0.37 1.5 0.86 25 Rank-A Rank-A 10 100 0.08 3.0 0.1 0
4.5 0.37 1.5 0.67 9 Rank-B Rank-A 11 100 0.08 3.0 0.1 0 4.5 0.37
2.5 0.67 7 Rank-B Rank-A 12 100 0.08 3.0 0.1 0 5.0 0.37 2.5 0.60 3
Rank-B Rank-A 13 100 0.08 3.0 0.1 0 4.5 0.37 2.0 0.67 9 Rank-B
Rank-A 14 100 0.08 3.0 0.1 0 5.0 0.37 2.0 0.60 7 Rank-B Rank-A 15
100 0.08 3.0 0.2 0 5.0 0.37 2.0 0.60 7 Rank-B Rank-A 16 100 0.08
3.0 0.2 0 5.0 0.37 3.0 0.60 4 Rank-B Rank-A 17 100 0.08 3.0 0.2 0
5.0 0.37 5.0 0.60 1 Rank-B Rank-A Note) BCG is an abbreviation of
(Ba.sub.0.6Ca.sub.0.4)SiO.sub.3 added as a second sub-component
functioning as a sintering aid.
[0130]
2 TABLE 2 Main component (moles) Sub-component (moles) Sample
BaTiO.sub.3 MgCO.sub.3 Si(BCG) V.sub.2O.sub.5 Yb.sub.2O.sub.3
Y.sub.2O.sub.3 MnCO.sub.3 CaZrO.sub.3 1 100 0.90 2.5 0.1 1.75 2.0
0.37 1.5 18 100 0.90 3.0 0.1 1.75 2.0 0.37 1.5 19 100 0.90 3.0 0.1
1.75 2.5 0.37 1.5 20 100 0.90 4.0 0.1 1.75 2.5 0.37 1.5 21 100 0.90
4.0 0.1 1.75 3.0 0.37 1.5 22 100 0.90 4.5 0.1 1.75 3.0 0.37 1.5 23
100 0.50 3.0 0.1 1.00 2.0 0.37 1.0 24 100 0.08 4.0 0.1 0 4.5 0.37
1.5 25 100 0.08 4.0 0.1 0 5.0 0.37 1.5 26 100 0.08 3.5 0.1 0 3.5
0.37 1.5 27 100 0.08 3.5 0.1 0 4.0 0.37 1.5 28 100 0.08 3.5 0.1 0
4.5 0.37 1.5 29 100 0.08 3.0 0.1 0 3.5 0.37 1.5 30 100 0.08 3.0 0.1
0 4.5 0.37 1.5 31 100 0.08 3.0 0.1 0 5.0 0.37 1.5 32 100 0.08 3.0
0.1 0 3.5 0.37 2.5 33 100 0.08 3.0 0.1 0 4.0 0.37 2.5 34 100 0.08
3.0 0.1 0 4.5 0.37 2.5 35 100 0.08 3.0 0.1 0 5.0 0.37 2.5 36 100
0.08 3.0 0.1 0 4.5 0.37 2.0 37 100 0.08 3.0 0.1 0 5.0 0.37 2.0 38
100 0.08 3.0 0.1 0 5.0 0.37 2.0 39 100 0.08 3.0 0.1 0 5.0 0.37 3.0
40 100 0.08 3.0 0.1 0 5.0 0.37 5.0 Comparative 100 0.08 3.0 0.2 0
2.0 0.37 1.0 Sample 1 C/D Yb.sub.2O.sub.3 + Variation (Molar
Y.sub.2O.sub.3 MTTF in life Sample ratio) (moles) Time Evaluation m
value Evaluation X8R 1 0.17 3.75 8 Rank-B 2.7 Rank-B Rank-A 18 0.19
3.75 11 Rank-B 2.9 Rank-B Rank-A 19 0.18 4.25 11 Rank-B 1.8 Rank-B
Rank-A 20 0.23 4.25 32 Rank-A 3.4 Rank-A Rank-A 21 0.21 4.75 18
Rank-A 5.2 Rank-A Rank-A 22 0.23 4.75 26 Rank-A 6.3 Rank-A Rank-A
23 0.26 3.0 30 Rank-A 2.9 Rank-A Rank-A 24 0.24 4.5 28 Rank-A 1.9
Rank-B Rank-A 25 0.23 5.0 18 Rank-A 4.8 Rank-A Rank-A 26 0.25 3.5
25 Rank-A 1.8 Rank-B Rank-A 27 0.23 4.0 28 Rank-A 3.7 Rank-A Rank-A
28 0.22 4.5 19 Rank-A 5.9 Rank-A Rank-A 29 0.22 3.5 25 Rank-A 7.2
Rank-A Rank-A 30 0.19 4.5 9 Rank-B 2.3 Rank-B Rank-A 31 0.18 5.0 15
Rank-B 2.4 Rank-B Rank-A 32 0.19 3.5 10 Rank-B 2.9 Rank-A Rank-A 33
0.18 4.0 4 Rank-B 1.1 Rank-B Rank-A 34 0.17 4.5 7 Rank-B 1.4 Rank-B
Rank-A 35 0.16 5.0 3 Rank-B 1.4 Rank-B Rank-A 36 0.18 4.5 9 Rank-B
1.7 Rank-B Rank-A 37 0.17 5.0 7 Rank-B 1.5 Rank-B Rank-A 38 0.17
5.0 7 Rank-B 1.4 Rank-B Rank-A 39 0.15 5.0 4 Rank-B -- Rank-B
Rank-A 40 0.13 5.0 1 Rank-B -- Rank-B Rank-A Comparative 0.31 2.0 4
Rank-B -- Rank-B Rank-A Sample 1 Note) BCG is an abbreviation of
(Ba.sub.0.6Ca.sub.0.4)SiO.sub.3 added as a second sub-component
functioning as a sintering aid. BCG contains 1 mol of Si atoms per
mol. C in C/D shows the number of moles of Si atoms in BCG. D in
C/D shows the total number of moles of the atoms in the
sub-components excluding the Si atoms and oxygen atoms in a
dielectric ceramic composition.
* * * * *